KR101863058B1 - METHOD AND APPARATUS FOR PURIFYING high purity BIOMETHANE WITH VARIABLE OPERATION - Google Patents

Abstract

The present invention relates to a biomethane purification method and a purification apparatus, comprising: compressing biogas; Separating the compressed biogas into a first residual stream and a first permeate stream; Introducing the first residual substream into a second polymer separator to separate into a second residual substream and a second permeate stream; Separating the second residual substream into a third residual substream and a third permeate stream, or introducing the second residual substream into a methane recovery unit; And separating the second permeate stream into a fourth residual permeate stream and a fourth permeate stream by introducing the second permeate stream into the fourth polymer separator, and a purification device capable of performing the same, can be provided .

Description

TECHNICAL FIELD [0001] The present invention relates to a high purity biomethane purification method and apparatus,

The present invention relates to a multi-stage membrane separation purification method and purification apparatus for purifying high purity biomethane from biogas.

Biogas produced by anaerobic digestion of food waste, organic waste, livestock wastewater, etc. is composed mainly of about 50% by volume to 75% by volume of methane, about 25% by volume to 50% by volume of carbon dioxide, Less than about 0.1 vol.% Oxygen or air, about 2,000 ppm to less than 8,000 ppm hydrogen sulfide, less than about 1 ppm to less than 40 ppm siloxane, less than about 50 ppm to less than 200 ppm ammonia, and the like.

Methane, a major component of biogas, contributes about 20 times more to global warming than carbon dioxide, and is designated as a greenhouse gas with a contribution of about 18 vol%, which is about 49 vol% of greenhouse gases, followed by carbon dioxide have.

However, since methane gas has an energy amount of 5,000 kcal / m ³ , it is evaluated as a clean and renewable energy source that can recycle resources that have no CO2 effect in terms of renewable energy. Technical research is being carried out continuously.

Methods of recycling biomethane in biogas include direct combustion, electricity production, supply to city gas, and use as fuel for automobiles. Various methods of utilization are selected and developed depending on the background and economics of methane generation.

Among these, the most economical and energy-efficient technology is to refine the methane concentration, that is, the energy content of the biogas to a high purity, to produce a methane gas fuel of 95 vol% or more that can be used as city gas or automobile fuel . Utilizing refined methane as city gas or automobile fuel is more economical than electricity generation. Recently, refined methane gas has been used as high purity fuel in Sweden and Germany and worldwide. In addition, the high purity methane gas can be used for conventional city gas appliances, natural gas vehicles, and the like, without replacing any equipment. Therefore, it is accepted as the next generation of clean bio energy. Sweden and Germany, which are advanced countries of renewable energy, are establishing national policy to replace automobile fuel and city gas with natural gas to biogas.

A variety of techniques have been developed for the separation process for making the biogas highly purified, the plant, and the operation conditions thereof. The high purity technology of biomethane consists of pretreatment technology to remove siloxane, ammonia, hydrogen sulfide, water and so on in biogas, where various components remain as impurities, and de-carbon dioxide separation technology to separate the remaining carbon dioxide and methane. Among them, the removal of carbon dioxide is largely based on the cryogenic method of separating directly at low temperature, the physical or chemical absorption using water or amines, the pressure swing adsorption method using zeolite or carbon molecular sorbent , Or membrane separation using a high methane-selective polymer membrane.

However, in the methane purification method using the absorption method or the adsorption method, the use of the carbon dioxide absorption process or the pressure swing adsorption (PSA) process in the above-described invention increases the installation cost of the plant, , A problem that a small-sized apparatus can not be constructed, a problem of poor purification efficiency, a complicated process, and a large amount of energy are consumed.

Therefore, research on membrane separation method which is easy to maintain in Korea and high methane purity among these methods is getting attention. The separation membrane method is advantageous in winter because it can be operated by dry method as compared with other separation method, and is environment friendly because it does not use toxic absorber, and the plant cost is low, operation cost is low, and scale up-scale down is easy .

Methane concentration and recovery rate are the most important targets in the separation membrane process, and the recovery rate is usually 60 ~ 75% in the first separation membrane process. In order to increase the recovery rate of methane, the separation membrane is connected in series in two stages, the permeate of the first separation membrane is incinerated and the permeate portion of the second separation membrane is recirculated, and the separation membrane is separated into two stages A three-stage membrane recycling process in which the permeate portion of the separation membrane is re-passed through the three-stage separation membrane and the untransmitted methane gas of the two-stage separation membrane is recycled is being developed.

For example, Japanese Laid-Open Patent Publication No. 2009-242773 discloses a three-step separation membrane process. Specifically, the methane concentration apparatus disclosed in the above document is a methane gas concentration apparatus for separating carbon dioxide from a gas mixture containing at least methane gas and carbon dioxide and concentrating the methane gas. By the separation membrane that has preferentially permeated carbon dioxide from the gas mixture, A first concentration device for concentrating methane gas, a second concentration device for further concentrating the methane gas by a separation membrane that preferentially permeates carbon dioxide from the non-permeable gas of the first concentration device, And a recovery device for recovering methane gas by a separation membrane that has preferentially permeated carbon dioxide. It is described that polyimide is most preferably used as the separation membrane.

The process conditions for temperature, film area, and the like are not specified. Therefore, when it is applied commercially, there is a problem that the specific feasibility of achieving high purity and high recovery rate of methane is low.

Biogas, on the other hand, has a diverse distribution of methane content depending on the source of food waste, organic waste, and livestock wastewater. In addition, even if they occur at the same site, the content of methane varies according to season depending on the property.

However, in the case of using the refining apparatus of the fixed operation type, it is difficult to cope with the change of the methane content in the raw material biogas, and it is difficult to purify the high purity biomethane suitable for use as automobile fuel with uniform purity have.

Research on techniques for multi-stage separation membrane process for solving such problems and stably refining biomethane from biogas at a high purity and a high recovery rate is continuing.

Japanese Patent Application Laid-Open No. 2009-242773

An object of the present invention is to provide a multistage membrane-separated biomethane purification method capable of variable operation with which biomethane can be purified from biogas stably with high purity.

It is an object of the present invention to provide a multi-stage membrane-separated biomethane purification apparatus capable of stable operation with high purity of biomethane from biogas and capable of variable operation.

One aspect of the present invention provides a method for producing a biogas, comprising: compressing a biogas; Separating the compressed biogas into a first residual stream and a first permeate stream; Introducing the first residual substream into a second polymer separator to separate into a second residual substream and a second permeate stream; Separating the second residual substream into a third residual substream and a third permeate stream, or introducing the second residual substream into a methane recovery unit; And separating the second permeate stream into a fourth residual permeate stream and a fourth permeate stream by injecting the second permeate stream into the fourth polymer separator.

The pressure ratio of the permeable portion to the remaining portion of the third polymer separation membrane may be 0.4 or more and 0.7 or less.

Separating the second residual sub-stream into a third residual stream and a third permeate stream, or introducing the second residual sub-stream into a methane recovery section, wherein the step of compressing the biogas Wherein the second residual stream is introduced into the methane recovery section when the content of methane is 68 vol% or more and 75 vol% or less based on 100 vol% of the total volume of the biogas, Is less than 60 vol% and less than 68 vol% with respect to 100 vol% of the total volume of the biogas, the second residual substream may be introduced into the third polymer separator.

Wherein the film area ratio of the first to fourth polymeric membranes is 1: 2 or more and 10 or less: 0.5 or more and 3 or less: 0.5 or more and 3 or less, and the membrane area ratio of the second polymeric membrane and the third polymeric membrane is 1: 0.3 or more 0.7 or less.

The method for purifying biomethane according to an embodiment of the present invention may further include the step of selectively introducing the second residual sub-stream into the third polymer separator to separate the third residual stream and the third permeate stream into a methane recovery unit The second residual substream in the third polymer separator is separated into a third residual substream and a third permeate stream, and when the third permeate stream is separated from the third polymer separator, To the compression step of the compressing step.

The purity of the purified biomethane may be 98% or more.

According to another aspect of the present invention, there is provided a biogas supply unit comprising: a biogas supply unit; A compression unit for compressing the biogas supplied from the biogas supply unit; The remaining substream of the first polymer separation membrane for removing carbon dioxide from the compressed gas in the compression section is connected to the second polymer separation membrane, the permeate stream of the second polymer separation membrane is connected to the fourth polymer separation membrane, And a purification section including a polymer separation membrane for gas separation, which is selectively connected to the methane recovery section or the third polymer separation membrane, in the residual secondary stream of the separation membrane.

The pressure ratio of the permeable portion to the remaining portion of the third polymer separation membrane may be adjusted to be 0.4 or more and 0.7 or less.

Wherein the film area ratio of the first to fourth polymeric membranes is 1: 2 or more and 10 or less: 0.5 or more and 3 or less: 0.5 or more and 3 or less, and the membrane area ratio of the second polymeric membrane and the third polymeric membrane is 1: 0.3 or more 0.7 or less.

The apparatus for purifying biomethane according to an embodiment of the present invention may further include a second-1 remaining sub-stream flow path for connecting the second polymer separation membrane and the methane recovery section and transferring the residual fraction stream of the second polymer separation membrane to the methane recovery section, ; And a second-2 residual stream flow passage connecting the second polymer separation membrane and the third polymer separation membrane, and transferring the remaining secondary stream of the second polymer separation membrane to the third polymer separation membrane.

The apparatus for purifying biomethane according to an embodiment of the present invention comprises: a first flow path opening / closing means provided in the second-1 residual flow path for regulating opening / closing of the second-1 remaining flow path; And a second flow path opening / closing means provided in the second-2 residual flow path passage for controlling the opening and closing of the second-2 residual flow path passage.

The apparatus for purifying biomethane according to an embodiment of the present invention includes a measurement sensor for measuring a content of methane in a biogas to be introduced into the compression unit; And a controller connected to the measurement sensor, the first flow path opening / closing means, and the second flow path opening / closing means.

Wherein the measurement sensor senses the amount of methane in the biogas to be supplied to the compression unit and converts the amount of methane into an electrical signal form to transfer the electrical signal to the controller, And to control opening and closing of the first flow path opening / closing means and the second flow path opening / closing means.

Wherein the controller is configured to control the amount of methane contained in the biogas to be supplied to the compression unit from the measurement sensor when the amount of methane contained in the biogas is greater than or equal to 68 vol% and less than or equal to 75 vol% The first flow path opening and closing means is opened and the second flow path opening and closing means is closed so as to close the first flow path opening and closing means and the second flow path opening and closing means, The second flow path opening / closing means is opened and the first flow path opening / closing means is closed when receiving a signal corresponding to 60 vol% or more and less than 68 vol% with respect to 100 vol% of the total volume of the biogas put into the compression portion And the opening and closing of the first flow path opening / closing means and the second flow path opening / closing means may be controlled.

The apparatus for purifying biomethane according to an embodiment of the present invention further includes a third permeate flow recirculation conduit connected to the third polymer separator and the compression section and recirculating the permeate stream of the third polymer separator to the compression section can do.

And a fourth residual substream recirculation flow channel connected to the fourth polymer separation membrane and the compression unit and recirculating the remaining substream of the fourth polymer separation membrane to the compression unit.

The apparatus for purifying biomethane according to an embodiment of the present invention may further include a cooling unit connected to the compression unit and the first polymer separator.

The method and the apparatus for purifying biomethane according to the present invention enable variable operation of the process according to the content of methane in the raw biogas and can stably purify high purity biomethane regardless of the concentration of methane in the raw biogas . Therefore, it is possible to purify various types of biomethane by only one facility, and it is possible to purify high purity biomethane stably even in an environment where the concentration of methane in the biogas changes depending on seasons.

In addition, it is possible to operate the process variable according to the purification situation, so that efficient separation can be performed according to the content of methane in the raw material biogas, and the lifetime of the biomethane purification apparatus can be increased and the maintenance cost can be reduced.

1 is a schematic diagram of a biomethane purification apparatus according to an embodiment of the present invention.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Whenever a component is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements, not the exclusion of any other element, unless the context clearly dictates otherwise. Also, singular forms include plural forms unless the context clearly dictates otherwise.

As used herein, unless otherwise defined, traces and amounts in the phrases "traces A and B" or "traces A and traces B" refer to traces of A and B Relative content.

Unless defined otherwise herein, the 'residual x-ray stream of polymer x separator' is used interchangeably with the 'x-x residual stream', and the 'x-ray polymer stream permeate stream' Used in combination.

As described above, the present invention provides a biomethane purification method capable of stably refining high-purity biomethane regardless of the concentration of methane in raw biogas, by allowing variable operation of the process depending on the content of methane in the raw biogas And a purification device.

Therefore, it is possible to purify various types of biomethane by only one facility, and it is possible to purify high purity biomethane stably even in an environment where the concentration of methane in the biogas changes depending on seasons.

In addition, according to the content of methane in raw material biogas, variable operation can be performed by a three-stage or four-stage separation membrane separation process, and efficient separation can be performed according to the content of methane in raw biogas. And the effect of reducing the maintenance cost can be expected.

Specifically, one aspect of the present invention provides a method for producing a biogas, comprising: compressing a biogas; Separating the compressed biogas into a first residual stream and a first permeate stream; Introducing the first residual substream into a second polymer separator to separate into a second residual substream and a second permeate stream; Separating the second residual substream into a third residual substream and a third permeate stream, or introducing the second residual substream into a methane recovery unit; And separating the second permeate stream into a fourth residual permeate stream and a fourth permeate stream by injecting the second permeate stream into the fourth polymer separator.

This is a purification method capable of stably refining biomethane with high purity of 98% or more, regardless of the content of methane in the raw material biogas, because the variable operation can be performed according to the change of the content of methane in the raw biogas. The first to fourth polymeric membranes may be made of a material or a material that transmits relatively more carbon dioxide than methane. Thus, when the biogas containing methane and carbon dioxide pass through the polymer separator, the composition of the permeate stream is controlled by a large amount of carbon dioxide and a relatively small amount of methane gas, and the composition of the residual sub- It is controlled by a trace amount of carbon dioxide.

Hereinafter, the method for purifying biomethane according to one embodiment of the present invention will be described in detail for each step.

The step of compressing the biogas is a step of compressing the biogas to an appropriate pressure to purify methane gas of high purity through a membrane separation process.

The compression of the compressing step is not limited to a specific method or a method using a specific apparatus, and any method can be used as long as the method or apparatus capable of compressing the gas is used.

At this time, the compression may be performed such that the pressure of the upper biogas is 3 bar or more and 100 bar or less, preferably 5 bar or more and 30 bar or less. If the pressure of the upper portion of the biogas is too small, the ratio of the upper pressure and the lower pressure of the separation membrane process (lower pressure / lower pressure) is lowered due to the lower selection of the polymer separation membrane. . If the pressure of the upper portion of the biogas is too high, the separation membrane may be plasticized by the carbon dioxide in the separation membrane process, thereby deteriorating the selectivity of the separation membrane. Accordingly, the purity and recovery rate of the finally purified methane may be lowered, or the separation membrane may be damaged.

The biomethane purification method according to an embodiment of the present invention may further include, after the compressing, regulating the temperature of the compressed biogas. Specifically, the temperature adjustment step may be a step of cooling the compressed biogas to remove the compression heat generated during the compression process to adjust the temperature of the biogas to a temperature range in which the separation membrane efficiency is good. to be.

The cooling of the cooling step is not limited to a specific method or a method using a specific apparatus, and any method can be used as long as it uses a method or device capable of cooling the gas.

At this time, cooling may be performed so that the temperature of the biogas becomes -20 캜 or more and 30 캜 or less. When the temperature of the cooled biogas is lowered to less than -20 ° C, the selectivity of the polymer separator is increased, but the cooling cost of the entire separator is increased, and there is a problem that the separator is frozen easily due to pressure have. When the temperature of the cooled biogas exceeds 30 캜, the selectivity of the polymer separator is significantly lowered, the methane recovery rate and purity are lowered, and the separator may be damaged due to heat.

The biogas in the compressing step may be pre-treated before the compressing step.

The biogas may include, for example, water, hydrogen sulfide, ammonia, siloxane, nitrogen, oxygen and the like in an amount of 0.0001 to 0.1 vol% based on 100 vol% of the total volume of the biogas as an impurity. The composition of the biogas includes, for example, about 60% to 75% by volume of methane, about 25% to about 40% by volume of carbon dioxide, methane and carbon dioxide mostly, hydrogen sulfide of about 1500 ppm to 2500 ppm, About 90 ppm or more and about 100 ppm or less, and about 3500 ppm or more and about 4500 ppm or less of moisture. Thus, a pretreatment for removing the impurities beforehand can be performed.

The pretreatment step may include dehumidification, desulfurization, deammonia and desiloxane treatment, and the like. In the case of performing the pretreatment of dry desulfurization and dry desiloxane, it may be preferable to perform the dehumidification treatment first in order to prevent various adsorbents such as desulfurizing agent and desiloxane agent from being entangled with moisture and deteriorating in adsorption capacity in a short time . On the other hand, when wet desulfurization or wet ammonia removal processes are introduced, it is preferable that the dehumidification treatment of the biogas is installed at the downstream end of the wet process in order to protect the permeation characteristics of the separation membrane. Here, the dehumidifying process may be performed by passing a raw material biogas through a cylindrical dehumidifier having a tube in which cooling water supplied from an external chiller is circulated, but the present invention is not limited thereto.

In addition, it is preferable that the dehumidifying treatment is performed so that the dew point temperature of the gas becomes 0 캜 or lower. More preferably, it can be carried out at -5 deg. C or higher and -50 deg. C or lower. If the dew point temperature of the dehumidified gas is too high, there is a possibility that the apparatus may be corroded in a continuous process, and the adsorption of various adsorbents may occur in subsequent steps, And there is a problem that the final produced methane gas can not be used as an automobile fuel.

The desulfurization treatment may be performed by dry desulfurization or wet desulfurization. Hydrogen sulphide contained in the biogas generates odor and causes corrosion of the machine, so it needs to be removed. At this time, the dry desulfurization process is environmentally friendly as compared with the wet desulfurization process, and an additional wastewater treatment process is unnecessary, thereby providing excellent process economics. However, the desulfurization treatment is not limited to the dry desulfurization treatment.

The desulfurization treatment may be performed by an iron oxide tower, and the desiloxane treatment may be performed by an impregnated activated carbon tower and a silica gel tower. The siloxane is combusted in the engine when it receives high heat generated in the compressor cylinder used in the purification process or when the finally produced methane gas is used as a fuel for automobiles and the like, so that silica (SiO ₂ ) is produced over a long period of time, It is necessary to remove solid matter from the surface of the engine such as a device or an automobile, because the solids adhere to the surface of the engine and shorten the parts life of the refining process apparatus or the engine. The iron oxide-based adsorbent adsorbs a large amount of hydrogen sulfide, and the hydrogen sulfide that has not been adsorbed can be adsorbed by the adsorbent for adsorbing activated carbon. At this time, some siloxanes may also be adsorbed on the impregnated activated carbon. The siloxane can be removed by adsorption on a silica gel column. Thus, the desulfurization and desiloxane process can be operated without degrading desulfurization and desiloxane performance even in an urgent situation, compared with a general desulfurization process composed of a single adsorbent, and each adsorbent has an advantage of complementing each other's functions.

After the pretreatment, the hydrogen sulfide concentration of the biogas may be 20 ppm or less and the concentration of the siloxane may be 0.1 ppb or less. When the final product contains hydrogen sulfide at a concentration exceeding 20 ppm, the product may be odorous, which may lead to corrosion of the equipment used when used as fuel. Also, when the concentration of siloxane exceeds 0.1 ppb, siloxane is burned in the engine when the methane gas is used as automobile fuel due to the high heat generated in the compressor cylinder used in the refining process, Silica (SiO ₂ ) adheres to the surface of the apparatus or the engine, which may shorten the parts life of the purification process apparatus or the engine.

Further, in addition to the desulfurization and desiloxane treatment, the deammonia treatment can be performed. Generally, the biogas can contain ammonia, and thus ammonia can be removed through de-ammonia treatment. The deammonia treatment may be carried out by precipitation in the form of ammonium sulfate through reaction with sulfuric acid, but is not limited thereto.

After the compression step, the biogas can be purified using a four-stage separation membrane filter capable of variable operation. Specifically, as described above, the compressed biogas is introduced into the first polymer separation membrane, Stream and a first permeate stream; Introducing the first residual substream into a second polymer separator to separate into a second residual substream and a second permeate stream; Separating the second residual substream into a third residual substream and a third permeate stream, or introducing the second residual substream into a methane recovery unit; And separating the second permeate stream into a fourth residual permeate stream and a fourth permeate stream by injecting the second permeate stream into the fourth polymer separator.

The compressed biogas can be purified through the separation membrane purification process as described above to purify the biomethane at a high purity and a high recovery rate and the variable operation can be performed according to the content of methane in the raw biogas. Even if the content is changed, high purity biomethane of 98% or more can be stably purified.

In addition, when the content of methane in the feedstock biogas is sufficient, it is possible to efficiently separate the feedstock according to the content of methane in the feedstock biogas by operating the process to bypass the third polymer separator. If unnecessary, The life of the third polymer separator may increase, leading to a reduction in the overall process cost. In addition, it is expected that the lifetime of the biomethane purification apparatus performing the purification process and the maintenance cost can be reduced.

For example, in the step of selectively injecting the second residual sub-stream into the third polymer separator to separate it into a third residual stream and a third permeate stream, or into a methane recovery section, the methane content in the raw biogas The second residual sub-stream may be directly recovered to the methane recovery section to purify high-purity biomethane. Therefore, since it is not necessary to pass through the third polymer separation membrane, it is possible to compress the biogas less in the compression step. Thus, an unnecessary increase in the process cost can be prevented. In addition, since the purification by the third polymer separation membrane is selectively performed, the lifetime of the third polymer separation membrane can be increased, thereby increasing the service life and maintenance cost of the purification apparatus.

On the other hand, when the content of methane in the raw biogas is low, the second residual substream may be introduced into the third polymer separator to purify the same again. Therefore, even if the content of methane in the raw material biogas is low, the biomethane can be purified with high purity.

As a specific, non-limiting example, the criterion that the second residual sub-stream is selectively introduced into the third polymer separator or directly into the methane recovery section is that the methane gas in the biogas in the step of compressing the biogas The second residual stream is introduced into the methane recovery section when the content of the methane gas is less than or equal to 68% by volume and less than or equal to 75% by volume with respect to the total volume of the biogas of 100% by volume, When the content is less than 60 vol% and less than 68 vol% with respect to 100 vol% of the total volume of the biogas, the second residual stream may be introduced into the third polymer separator. However, the present invention is not limited thereto, but may be otherwise controlled.

The control of the flow of the second residual sub-stream according to the content of methane in the raw biogas as described above can be exemplified by actively responding to the change of the methane content in the raw biogas, Can be performed by an automation system. Specifically, during purification of the biogas, the content of methane in the raw biogas is qualitatively and quantitatively analyzed and detected through a measurement sensor, and the flow of the second residual sub-stream is variably measured based on the detection result received from the measurement sensor To be introduced into the third polymer separation membrane or directly into the methane recovery section.

As another example, in a range in which the purity of the methane gas to be finally purified is maintained at 98% or more, a part of the second residual sub-stream is introduced into the third polymer separation membrane and the remaining part is directly introduced into the methane recovery section It is also within the scope of the present invention to perform purification.

The third polymer separator may be added to the second polymer separator to selectively function depending on the content of methane in the raw biogas or the refining state of the biogas in the process of operating the process. Therefore, the biomethane purification method of the present invention can be operated variably according to the purification condition of the biogas, so that the process operation becomes flexible, and it is possible to cope with various situations in a single process, The methane gas can be stably purified. In addition, since the purification by the third polymer separation membrane is selectively performed, the lifetime of the third polymer separation membrane can be increased, thereby increasing the service life and maintenance cost of the purification apparatus.

In this case, the membrane area ratio of the first to fourth polymer membranes (first polymer separator: second polymer separator: third polymer separator: fourth polymer separator) is 1: 2 to 10: 0.5 to 3: 0.5 Or more and 3 or less.

In one embodiment of the present invention, the membrane area of the second polymer separation membrane may be larger than the membrane area of the third polymer separation membrane. Therefore, when the methane concentration in the raw biogas is high, the second polymer separation membrane plays a major role in biogas purification, and even if the second residual stream does not pass through the third polymer separation membrane, Can be separated into high purity.

More specifically, the membrane area ratio of the second polymer separation membrane and the third polymer separation membrane (second polymer separation membrane: third polymer separation membrane) may be 1: 0.3 or more and 0.7 or less. In the case of adjusting to the above range, there is an advantage that the purity and recovery rate of methane can be increased by the reduced process cost as the area ratio of the third polymer membrane is smaller than that of the second polymer membrane.

In the method of manufacturing biomethane according to an embodiment of the present invention, the second residual stream is selectively introduced into the third polymer separator and separated into the third residual stream and the third permeate stream, or the methane recovery unit The second residual substream in the third polymer separator is separated into the third residual substream and the third permeate stream, and when the second residual substream is separated into the third polymer separator, To the compression step of the compressing step. As a result, methane remaining in the permeate stream of the third polymer separator can be further recovered, thereby further improving the purity of the finally purified methane gas.

Hereinafter, other process conditions of a series of refining processes performed after the compressing step will be described.

In a series of refining processes after the compression, the permeation force of the permeate portion and the residual portion of each of the first polymer separator, the second polymer separator, the third polymer separator, and the fourth polymer separator, A flow is formed. At this time, the pressure ratio (permeated portion / residual portion) of the permeable portion to the remaining portion of the third polymer separation membrane may be 0.4 or more and 0.7 or less. When the pressure ratio of the permeable portion to the remaining portion of the third polymer separation membrane satisfies the above range, the permeability of the third polymer separation membrane, which functions selectively depending on the purification condition, can be prevented from being lowered, have. Thus, upon further purification of the second residual substream through the third polymer separator membrane, the methane separation efficiency is improved, allowing the methane in the second residual substream to be further concentrated to the desired level. Thus, the concentration of methane in the final residual third stream is sufficiently concentrated, and the purity of the finally recovered biomethane can be remarkably improved. On the other hand, in the case of deviating from the above range, it was not possible to stably refine the biomethane to a purity of 98% or more in an environment where the methane content in the raw material biogas changes, as confirmed in the following embodiments.

Meanwhile, the separation membrane material used in the separation membrane process for separating biomethane according to an embodiment of the present invention may be a medium-selective polymer material selected from a highly selective material having a carbon dioxide / methane selectivity of 20 or more and 100 or less, , It is preferable that it is 20 or more and 60 or less. The polymer separator may be preferably an amorphous or semi-crystalline polymer. Examples of the polymer separator include polyimide, polyamide, polyether sulfone, polysulfone, polycarbonate But are not limited to, polycarbonate, polyethylene terephthalate, cellulose acetate, poly (phenylene oxide), polysiloxane, poly (ethylene oxide), polypropylene (Poly (propylene oxide)), and mixtures thereof. In addition, a material such as polyimide synthesized with a low selectivity in order to increase the permeability of carbon dioxide in the process of manufacturing a membrane material may be included.

At this time, in the case of a polymer membrane material which is processed into a composite membrane or a hollow fiber membrane by an asymmetric structure by a phase transfer method or a thin film coating method, the carbon dioxide permeability may be preferably 10 GPU or more and 1,000 GPU or less, 100 GPU or more and 1,000 GPU or less may be preferable. The unit of area (cm ² ), the unit pressure (mmHg) of the separation membrane, and the unit pressure (mmHg) of the separation membrane are represented by the gas permission unit (1 GPU = (10 ^-6 cm m ³ ) / (cm ² sec sec mm mmHg) And the volume (cm < ³ >) of carbon dioxide permeated per unit time (sec).

The separation membrane material used in one embodiment of the present invention has a high selectivity of carbon dioxide / methane of 40 or more, such as polyimide, polyether sulfone and the like, unlike the three- Various membrane materials can be applied to materials having medium selectivity ranging from 20 to 34 such as poly sulfone, cellulose acetate, and polycarbonate. Polyether sulfone and polyimide used in membrane materials have high selectivity but may have a low carbon dioxide permeability and poly sulfone and the like have medium selectivity but carbon dioxide (Polyimide) is superior to polyimide, so it can be selected among various membranes. When a separator material having too low selectivity is used, a large amount of gas is recycled in order to obtain methane of high purity, which may cause a problem in that a large amount of energy is required. In case of using a material having too high selectivity, the permeability tends to be low. The separation membrane process using such a material requires a large amount of high-purity methane produced and a large amount of recycled material, , Which may lead to an increase in the scale of the process. For the above reasons, a membrane material having intermediate selectivity can be used. Among them, a polymer material such as poly sulfone, which has higher resistance to plasticization due to pressure than polyimide, can be used But is not limited thereto.

Hereinafter, a biomethane purification apparatus according to an embodiment of the present invention will be described with reference to FIG. However, the biomethane purification apparatus according to an embodiment of the present invention is not limited to only the configuration of FIG. 1, and various modifications may be made within the scope of the technical idea of the present invention.

According to another aspect of the present invention, there is provided a biogas supply apparatus comprising: a biogas supply unit; A compression unit 41 for compressing the biogas supplied from the biogas supply unit 10; The remaining substream of the first polymer separator 51 for removing carbon dioxide from the compressed gas in the compressing section 41 is connected to the second polymer separator 52 and the permeate stream of the second polymer separator 52 The residual stream of the second polymer separator 52 is connected to the fourth polymer separator 54 and the third polymer separator 53 is selectively connected to the methane recovery unit And a purification section (50) containing the biomethane purification device. The methane recovery unit (not shown) may be a device connected to the second polymer separator 52 and / or the third polymer separator 53 to recover purified biomethane as an end product, It is not limited to a specific device as long as it is an apparatus for recovering as a final product.

In the biomethane refining apparatus according to an embodiment of the present invention, the biogas supply unit 10 for supplying the biogas is not limited to bio-gas generated from a food waste treatment plant, a sewage sludge treatment plant, a landfill, The apparatus for introducing the gas into the purification apparatus of the present invention may be a known apparatus such as a blower.

The apparatus for purifying biomethane according to an embodiment of the present invention may include a dehumidifying unit 20 and a pretreatment unit 30 for removing sulfur, ammonia, and siloxane from the dehumidified gas. The dehumidifying part 20 is not limited to a specific configuration, and may be, for example, a cylindrical dehumidifying device having a tube in which cooling water supplied from an external cooler is circulated. If the pre-treatment unit 30 adopts a wet desulfurization and de-ammonia system, the dehumidifying unit 20 may be installed to perform a backward step of the pre-treatment unit 30 have.

The pretreatment unit 30 for removing sulfur, ammonia, and siloxane from the dehumidified gas in the dehumidifying unit 20 may include a desulfurization unit and a desiloxane unit. The desulfurization unit may include an iron oxide tower, The desiloxane device may include an iron oxide column, an impregnated activated carbon column, and a silica gel column. At this time, each device for the desiloxane may be connected in series or in parallel. The iron oxide-based adsorbent adsorbs a large amount of hydrogen sulfide, and the hydrogen sulfide that has not been adsorbed can be adsorbed using an impregnated activated carbon adsorbent. At this time, some siloxanes may be adsorbed on the impregnated activated carbon. Such desulfurization and desiloxane units can be operated without degradation of desulfurization and desiloxane performance even under urgent conditions, as compared with general desulfurization and desiloxane units composed of a single adsorbent. Each of the adsorbents complements each other's functions, And the siloxane can be efficiently removed.

The compression section (41) is not limited to a device capable of compressing a gas, and can be employed without being limited to a specific device.

In the compression unit 41, biogas compression may be performed so that the pressure of the upper biogas may be 3 bar or more and 100 bar or less, preferably 5 bar or more and 30 bar or less. If the pressure of the upper portion of the biogas is too small, the ratio of the upper pressure and the lower pressure of the separation membrane process (lower pressure / lower pressure) is lowered due to the lower selection of the polymer separation membrane. . If the pressure of the upper portion of the biogas is too high, the separation membrane may be plasticized by the carbon dioxide in the separation membrane process, thereby deteriorating the selectivity of the separation membrane. Accordingly, the purity and recovery rate of the finally purified methane may be lowered, or the separation membrane may be damaged.

The apparatus for purifying biomethane according to an embodiment of the present invention may further include a temperature regulator for regulating the temperature of the compressed biogas, and the temperature regulator may be a cooling unit. This can serve to regulate the temperature of the biogas in a temperature range in which the separation membrane efficiency is good by removing the compression heat generated during the compression process. The cooling unit 42 is not limited to a specific apparatus, and any apparatus that can cool the gas can be used.

The temperature of the biogas compressed by the cooling unit 42 may be cooled to -20 캜 or more and 30 캜 or less. When the temperature of the cooled biogas is lowered to less than -20 ° C, the selectivity of the polymer separator is increased, but the cooling cost of the entire separator is increased, and there is a problem that the separator is frozen easily due to pressure have. When the temperature of the cooled biogas exceeds 30 캜, the selectivity of the polymer separator is significantly lowered, the methane recovery rate and purity are lowered, and the separator may be damaged due to heat.

The material and physical properties of the separation membrane of the biomethane purification apparatus according to an embodiment of the present invention, the membrane area ratio of each separation membrane, the pressure ratio of the permeation unit to the remaining portion of the third polymer separation membrane, and the like are as described above.

Hereinafter, the biomethane purification apparatus according to one embodiment of the present invention will be described in detail with reference to the biomethane purification apparatus through the biomethane purification apparatus according to an embodiment of the present invention.

The raw material biogas is supplied from the biogas supply unit 10 and the water, sulfur, siloxane, and ammonia are removed through the dehumidifying unit 20 and the pretreatment unit 30. [ Thereafter, the pretreated biogas is adjusted to a pressure and a temperature suitable for the purification of the biogas via the compression unit 41 and the cooling unit 42, and then the purified biogas is supplied to the purification unit 50.

The biogas introduced into the purification section 50 is separated into a first residual stream having a high methane concentration and a first permeate stream having a high concentration of carbon dioxide in the first polymer separation membrane 51. The first permeate stream is discharged to a carbon dioxide recovery unit (not shown), and the first residual stream is introduced into the second polymer separator 52. In the second polymer separator (52), the first residual stream is separated into a second residual stream and a second permeate stream. Methane is further concentrated through the second polymer separator (52) The concentration of methane in the stream can be further increased.

The second residual substream may be a second-1 residual substream (not shown) that selectively connects the second polymer separator 52 and the methane recovery unit (not shown) according to the methane content in the raw biogas. (Not shown) through the first and second polymer separation membranes 52 and 53 or through the second-2 residual stream flow passages 61 connecting the second polymer separation membranes 52 and the third polymer separation membranes 53, And can be introduced into the polymer separator 53. The first-second flow-through flow path 62 and the second-2 residual flow path flow path 61 are provided with a first flow path opening / closing means 72 and a second flow path opening / closing means 71, respectively, The second sub stream residual flow passage 62 and the second sub stream residual flow passage 61 can be selectively opened and closed and the flow of the second residual sub stream can be adjusted according to the opening and closing control. The flow path opening / closing means 71, 72 may be a valve provided in the flow path and capable of opening and closing the flow path, but it is needless to say that any means can be employed as long as the flow path can be opened and closed. The connection of the specific polymer separation membrane and the compression section 41 in the present invention means that not only the specific polymer separation membrane and the compression section 41 are directly connected to each other through the flow path but also the specific polymer separation membrane, To the compression section (41).

Specifically, the second residual sub-stream may have a purity of 98 vol% or more, which is a level suitable for use as city gas or automobile fuel depending on the influence of the content of methane gas in the raw material biogas or the like, It may have low purity.

If the content of methane gas in the feedstock biogas is sufficient, the second residual stream may have a purity of at least 98 vol.%, Which is a level suitable for use with city gas or automotive fuel, in which case the second residual sub- (Not shown) directly through the second-1 remaining-stream-flow channel 62, and 98 vol.% Of high-purity biomethane can be immediately recovered.

On the other hand, when the content of the methane gas in the raw biogas is insufficient, the second residual stream is introduced into the third polymer separator through the second-2 residual stream passage 61, , It can be purified into a third residual substream of high purity whose content of methane is adjusted to a sufficient level. The third residual stream is introduced into the methane recovery section to recover high purity biomethane. In this case, the third permeate stream separated from the third polymer separator passes through the third permeate flow recirculation passage 81 connecting the third polymer separator 53 and the compression section 41 to the compression section 41 ) Through which the remaining methane in the third permeate stream can be recovered.

The criterion that the second residual substream is selectively introduced into the third polymer separator 53 or directly into the methane recovery unit (not shown) is, for example, It can be determined by the content of methane in the biogas. That is, when the content of methane in the feedstock biogas is sufficiently high, the second residual substream is directly fed to a methane recovery unit (not shown) without further purification due to introduction into the third polymer separator 53, Gt; biomethane < / RTI > This operation can be performed when biomethane having a purity of 98% or more, which is a sufficient level to be used for automobile fuel, city gas, etc., can be purified through purification to the second polymer separation membrane. On the other hand, when the content of methane in the raw biogas is not sufficient to purify high purity biomethane by the two-stage separation membrane process, the second residual substream can be introduced into the third polymer separator 53. Thus, the high purity biomethane can be purified through further purification through the third polymer separation membrane.

The criterion in which the second residual substream is selectively introduced into the third polymer separator 53 or directly into the methane recovery unit (not shown) is specifically a raw biomass introduced into the compression unit 41, If the content of methane gas in the gas is not less than 68% by volume and not more than 75% by volume based on 100% by volume of the raw material biogas, the second residual stream is introduced into the methane gas recovery device, The second residual substream may be introduced into the third polymer separator when the content of the methane gas in the feedstock biogas is less than 60% by volume and less than 68% by volume based on 100% by volume of the raw material biogas. have. However, the present invention is not limited thereto, but may be otherwise controlled.

The control of the flow of the second residual stream according to the content of methane in the raw biogas can be performed by an automation system as shown in FIG. Specifically, a measurement sensor (not shown) for sensing in real time a value obtained by quantitatively and qualitatively analyzing the content of methane in the raw material biogas to be supplied to the compression section 41 is provided in the flow path between the pre- processing section 30 and the compression section 41 73 may be provided. The measurement sensor 73 is electrically connected to the controller 74 to transmit the measured methane content to the controller 74 in the form of an electrical signal. The controller 74 receiving the signal judges the signal received from the measurement sensor 73 in accordance with a preset reference and operates so that the flow path opening and closing means 71 and 72 are selectively opened and closed. More specifically, when the content of methane in the raw material biogas is not less than 60% by volume and less than 68% by volume with respect to 100% by volume of the total volume of the raw material biogas, the second flow path opening / Closing signal is transmitted to the controller 74 so that the opening and closing of the flow path opening and closing means 71 and 72 are controlled so that the second residual flow stream is supplied to the third polymer And then introduced into the separation membrane 54. On the other hand, when the content of methane in the raw material biogas is 68 vol% or more and 75 vol% or less with respect to 100 vol% of the total volume of the raw biogas, the second charged opening and closing means 71 is closed from the measurement sensor 73 The opening and closing of the flow path opening and closing means 71 and 72 is controlled so that an opening signal of the first flow path opening and closing means 72 is transmitted to the controller 74, ). ≪ / RTI >

It is needless to say that the measurement sensor and the controller can appropriately employ the well-known measurement apparatus and controller.

In another operation mode of the purification of the biomethane using the purification apparatus according to another embodiment of the present invention, a portion of the second residual sub- 3 polymer separator, and the remainder is directly introduced into the methane recovery section.

That is, the third polymer separation membrane may be added to the second polymer separation membrane and selectively function according to the content of methane in the raw material biogas, or the refining state of the biogas in the middle of the operation of the process. Therefore, the biomethane purification apparatus of the present invention can be operated variably according to the purification condition of the biogas, so that the process operation becomes flexible, and it is possible to cope with various situations in one process, The methane gas can be stably purified. In addition, since the purification by the third polymer separation membrane is selectively performed, the lifetime of the third polymer separation membrane can be increased, thereby increasing the service life and maintenance cost of the purification apparatus.

When the second residual sub-stream is introduced into the third polymer separator 53, the third residual sub-stream separated from the third polymer separator 53 is introduced into a methane recovery unit (not shown) And the third permeate stream is recycled to the compression section 41 through the third permeate flow recirculation flow path 81 connecting the third polymer separation membrane 53 and the compression section 41, 3 methane remaining in the permeate stream can be recovered.

Meanwhile, the second permeate stream is introduced into the fourth polymer separator 54, and passes through the permeate stream purification section.

The second permeate stream introduced into the fourth polymer separator 54 is separated into the fourth residual stream and the fourth permeate stream in the fourth polymer separator 54. The fourth permeate stream includes carbon dioxide at a high concentration and is discharged to a carbon dioxide recovery unit (not shown), and the fourth residual substream is connected to the fourth polymer separator 54 and the compression unit 41 Can be recycled to the compression section (41) through the fourth residual sub-stream recirculation flow path (82).

Hereinafter, preferred embodiments and comparative examples of the present invention will be described. However, the following examples are only a preferred embodiment of the present invention, and the present invention is not limited to the following examples.

Example

Methane gas was purified from the biogas using a module as shown in Fig. 1, which was made of a polysulfone separator. The biogas used for the separation was pretreated to contain hydrogen sulfide in an amount of 20 ppm or less and siloxane in an amount of 0.1 ppb or less and dehumidified to a dew point temperature of -5 캜 and then controlled to 20 캜.

Biogas having different amounts of methane gas were supplied to the purification section over time and biogas (first biogas and second biogas) having different methane gas contents were supplied to the purification section at intervals of 20 minutes as follows . The feed flow rates were all 100 L / min. Here, the volume% refers to a volume percentage with respect to 100 volume% of the total volume of the supplied biogas.

About 72% by volume of the first biogas: methane, about 28% by volume of carbon dioxide,

About 65% by volume of the second biogas: methane, about 35% by volume of carbon dioxide,

Then, the pressure of the pretreated biogas supplied to the purification part was adjusted to be 11 bar, the permeation part pressure of the second polymer separation membrane was 5 bar, the permeation part pressure of the third polymer separation membrane was 1 bar, the permeation part pressure of the fourth polymer separation membrane was 1 bar Respectively. The pressure ratio of the permeable portion to the remaining portion of the third polymer separation membrane was kept at 0.5.

The membrane separation process was carried out by supplying the biogas at a rate of 100 L / min with the area ratio of the first polymer membrane area, the second polymer membrane area, the third polymer membrane area and the fourth polymer membrane area being 1: 6: 2: Respectively.

In addition, the first flow path switching valve and the second flow path switching valve are selectively opened or closed according to the content of the raw material biogas supplied to the purification section.

Specifically, when the first biogas is supplied, the second residual substream is directly recovered to the methane recovery section, and when the second biogas is supplied, the second residual substream is introduced into the third polymer separation membrane.

The purity of the methane in the second polymer separation membrane residual stream or the third polymer separation membrane residual stream recovered to the finally recovered gas, that is, the methane recovery section, was measured after performing the above-described biomethane purification for 10 hours.

Comparative Example 1

The biomethane was purified in the same manner as in Example 1, except that the pressure ratio (permeation / residual) of the permeation portion to the remaining portion of the third polymer separation membrane was kept at 0.3.

Comparative Example 2

The biomethane was purified in the same manner as in Example 1 except that the pressure ratio of the permeation portion to the remaining portion of the third polymer separation membrane (permeation portion / residual portion) was kept at 0.8.

Experimental Example

In order to confirm the methane separation efficiency of the biomethane purification method according to the present invention, after performing the above Example 1, Comparative Example 1 and Comparative Example 2, the concentration of methane and the concentration of carbon dioxide in the finally recovered gas were analyzed The results are shown in Table 1 below.

In Table 1, "%" means the volume percentage of methane or carbon dioxide to 100 volume% of the total volume of each corresponding stream. Example 1, Comparative Example 1, and Comparative Example 2:
Methane recovery section  Recovered Second  Polymer membrane Residual portion  or Third  Polymer membrane remnant Example 1 Methane concentration (%) 99.3% Carbon dioxide concentration (%) 0.7% Comparative Example 1 Methane concentration (%) 94.7% Carbon dioxide concentration (%) 5.3% Comparative Example 2 Methane concentration (%) 95.6% Carbon dioxide concentration (%) 4.4%

As shown in Table 1, in the case of Example 1, when the residual substream of the second polymer separation membrane is selectively introduced into the third polymer separation membrane according to the methane content in the feed biogas or immediately recovered to the methane recovery section, It was possible to purify the biomethane stably with a purity of 98% or more while actively responding to the change of the methane concentration of the gas. In addition, biomethane could be purified with a methane recovery rate of 99% or more.

On the other hand, in the case of Comparative Examples 1 and 2, when the pressure ratio of the permeable portion to the remaining portion of the third polymer membrane is out of the range of the present invention, the purity of 98% or more in the purification environment where the methane content in the raw material biogas changes, It was impossible to purify biomethane.

10: Biogas supply part 20: Dehumidification part
30: preprocessing section 41: compression section
42: cooling section 50: refining section
51: first polymer separator 52: second polymer separator
53: Third polymer separator 54: Fourth polymer separator
61: 2-2 Residual sub-stream flow passage 62: 2-1 Residual sub-stream flow passage
71: second flow path opening / closing means 72: first flow path opening /
81: Third Transmission Port Stream Recirculation Flow
82: Fourth residual sub-stream recirculation flow path

Claims (16)

Compressing the biogas;
Separating the compressed biogas into a first residual stream and a first permeate stream;
Introducing the first residual substream into a second polymer separator to separate into a second residual substream and a second permeate stream;
Separating the second residual substream into a third residual substream and a third permeate stream, or introducing the second residual substream into a methane recovery unit; And
Separating the second permeate stream into a fourth residual stream and a fourth permeate stream by injecting the second permeate stream into a fourth polymer separator,
Separating the second residual sub-stream into a third residual stream and a third permeate stream, or introducing the second residual sub-stream into a methane recovery section, wherein the step of compressing the biogas Wherein the second residual stream is introduced into the methane recovery section when the content of methane is not less than 68 vol% and not more than 75 vol% with respect to 100 vol% of the total volume of the biogas, When the content of the second residual substream is 60 vol% or more and less than 68 vol% based on 100 vol% of the total volume of the biogas, the second residual substream is introduced into the third polymer separator,
The pressure ratio of the permeable portion to the remaining portion of the third polymer separator is 0.4 or more and 0.7 or less,
The membrane area ratio of the first to fourth polymer membranes is 1: 2 or more and 10 or less: 0.5 or more and 3 or less: 0.5 or more and 3 or less,
Wherein the membrane area ratio of the second polymer separator and the third polymer separator is 1: 0.3 or more and 0.7 or less,
Biomethane purification method.
delete delete delete The method of claim 1,
Separating the second residual substream into a third residual substream and a third permeate stream or introducing the third residual substream into a methane recycle section, and introducing the second residual substream into the third polymer separator ,
In the third polymer separator, the second residual sub-stream is separated into a third residual sub-stream and a third permeate stream,
Further comprising the step of recirculating said third permeate stream prior to the compressing step of said compressing step.
Biomethane purification method.
The method of claim 1,
Wherein the purified biomethane has a purity of 98%
Biomethane purification method.
A biogas supply unit;
A compression unit for compressing the biogas supplied from the biogas supply unit;
The remaining substream of the first polymer separation membrane for removing carbon dioxide from the compressed gas in the compression section is connected to the second polymer separation membrane, the permeate stream of the second polymer separation membrane is connected to the fourth polymer separation membrane, And a purification section including a polymer separation membrane for gas separation, which is selectively connected to the methane recovery section or the third polymer separation membrane,
The purification unit may include:
A second-1 remaining sub-stream flow passage connecting the second polymer separation membrane and the methane recovery section and transferring the remaining sub stream of the second polymer separation membrane to the methane recovery section;
A second-2 residual stream flow passage connecting the second polymer separation membrane and the third polymer separation membrane and transferring the remaining fraction stream of the second polymer separation membrane to the third polymer separation membrane;
A first flow path opening / closing means provided in the 2-1 remaining flow downstream flow path for regulating opening and closing of the 2-1 remaining flow downstream flow path;
A second flow path opening / closing means provided in the second-2 residual flow path flow path for regulating opening / closing of the second-2 residual flow path flow path;
A measurement sensor for measuring a content of methane in the biogas introduced into the compression unit; And
And a controller connected to the measurement sensor, the first flow path opening / closing means, and the second flow path opening / closing means,
Wherein the measurement sensor senses the amount of methane in the biogas to be supplied to the compression unit and converts the content of the methane into an electrical signal form to transfer the electrical signal to the controller, And controls opening and closing of the first flow path opening / closing means and the second flow path opening / closing means,
Wherein the controller is configured to control the amount of methane contained in the biogas to be supplied to the compression unit from the measurement sensor when the amount of methane contained in the biogas is greater than or equal to 68 vol% and less than or equal to 75 vol% The first flow path opening and closing means is opened and the second flow path opening and closing means is closed so as to close the first flow path opening and closing means and the second flow path opening and closing means, The second flow path opening / closing means is opened and the first flow path opening / closing means is closed when receiving a signal corresponding to 60 vol% or more and less than 68 vol% with respect to 100 vol% of the total volume of the biogas put into the compression portion The opening and closing of the first flow path opening / closing means and the opening / closing of the second flow path opening /
The pressure ratio of the permeable portion to the remaining portion of the third polymer separator is adjusted to be 0.4 or more and 0.7 or less,
The membrane area ratio of the first to fourth polymer membranes is 1: 2 or more and 10 or less: 0.5 or more and 3 or less: 0.5 or more and 3 or less,
Wherein the membrane area ratio of the second polymer separator and the third polymer separator is 1: 0.3 or more and 0.7 or less,
Biomethane purification system.
delete delete delete delete delete delete delete 8. The method of claim 7,
And a third permeate flow recirculation passage connected to the third polymer separator and the compression section for recirculating the permeate stream of the third polymer separator to the compression section.
Biomethane purification system.
8. The method of claim 7,
And a fourth residual substream recirculation flow channel connected to the fourth polymer separation membrane and the compression section and recirculating the remaining substream of the fourth polymer separation membrane to the compression section.
Biomethane purification system.

Images